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How do food scientists determine caloric content?

CplFerro

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CplFerro
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Jul 30, 2005
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I've wondered this for a while now. How do food scientists determine the caloric content per unit of any given food or beverage? I have no idea how this is done - do you?
 
The school science book answer is they burn it in oxygen in a calorimeter that measures the amount of heat produced very accurately. There are probably more advanced methods that I'm unaware of.
 
they work on the general taste scale, the nicer it tastes, the more calories it has.
 
Ivor has it- essentially a measure of how much the heat output of a specific mass of the material being tested raise the temperature of a specific amount of water. Try www.dogpile.com enter calorimeter, hit fetch, go to web locs for details.
 
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They used to use calorimeters, but nowadays it's simple book keeping. In Canada, anyway. I'm pretty sure it's the same system for the US, don't know about Europe.

4 Cal/gram for sugar/starch/protein
9 Cal/gram for fats/oils
7 Cal/gram for alcohol

No calories from fiber, which would have ~4 Cal/gram if you burned it. For example, a log has no Calories for a human, but releases plenty of heat when burned.
 
The Wikipedia article on calorimeters is actually pretty good - I was originally going to reply that one uses a bomb calorimeter (I've used them in the past) but the Wiki article lists many methods.
 
Ivor the Engineer said:
The school science book answer is they burn it in oxygen in a calorimeter that measures the amount of heat produced very accurately. There are probably more advanced methods that I'm unaware of.
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Thanks Ivor, et al. So, they really do burn the food to determine caloric content...

Cpl Ferro
 
CplFerro said:
Thanks Ivor, et al. So, they really do burn the food to determine caloric content...

Cpl Ferro
Click to expand...

They used to. From the USDA
Calorie values are based on the Atwater system for determining energy values. The factors used in the calculation of energy in the database are given in the food description file of the USDA Nutrient Database for Standard Reference, Release. The basis and derivation of these factors are described in

Merrill, A.L. and Watt, B.K. 1973. Energy Value of Foods...Basis and Derivation. Agriculture Handbook No. 74. U.S. Government Printing Office. Washington, DC. 105p.

This reference is out of print, but a scanned copy is viewable on our home page. It may also be available at many university libraries. The Atwater system uses specific energy factors which have been determined for basic food commodities. These specific factors take into account the physiological availability of the energy from these foods. The more general factors of 4-9-4 were developed from the specific calorie factors determined by Professor Atwater and associates. For multi-ingredient foods which are listed by brand name, calorie values generally reflect industry practices of calculating calories from 4-9-4 kcal/g for protein, fat, and carbohydrate, respectively, or from 4-9-4 minus insoluble fiber. The latter method is frequently used for high-fiber foods because insoluble fiber is considered to provide no physiological energy. If the calorie factors are blank or zero for an item in the Database, energy was calculated by recipe from ingredients or was supplied by the manufacturer.
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From Answers.com:

Physiological Fuel Values of Foods

The physiological fuel value of a food or a food component may be determined by measuring the heat of combustion of the food in a calorimeter and then multiplying the heat of combustion by correction factors for incomplete digestion and incomplete oxidation of the food in the body. In about 1900, Wilbur Olin Atwater and his associates at the Connecticut (Storrs) Agriculture Experiment Station used this approach to determine the physiological fuel values of a number of food components (i.e., the protein, fat, and carbohydrate isolated from various foods). They determined factors appropriate for individual foods or groups of foods, and they proposed the general physiological fuel equivalents of 4.0, 8.9, and 4.0 kcal per gram of dietary protein, fat, and carbohydrate respectively for application to the mixed American diet. These factors are commonly rounded to 4, 9, and 4 kcal per gram (17, 36, and 17 kJ per gram) respectively for protein, fat, and carbohydrate. The conversion factors determined by Atwater and his associates remain in use in the twenty-first century, and energy values of foods are calculated using these factors. The energy values (physiological fuel values) reported in food composition tables are commonly estimated by determination of the proximate composition of each food (i.e., the water, protein, fat, carbohydrate, and ash contents) followed by multiplication of the amount of each energy-yielding component by the appropriate conversion factor.
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Some of the foods on the USDA database list carbohydrates 'by difference' (IIRC). What I think this means is that they burn a sample of the food, figure out the energy/g, measure the nitrogen, meausre the fat, and calculate the protein and fat content from those values.
From the nitrogen values and fat values they calculate the expected fat and protein amounts and kcals, and subtract those kcal values from the total energy to get the carb kcals. When done this way, the value for carb energy does include fiber.

(Which is why we have the horrible pet food melamine contamination problem right now - apparently the despicable Chinese company dosed some plain wheat flour with a non-protein nitrogen-containing industrial waste, melamine, which would be falsely counted as protein, and sold it falsely as wheat gluten or rice protein isolate. And the recalls are not done yet according to petconnection.com.)
 
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And drinking a diet cola cancels out the calories of a cheeseburger!

It's true. :)
 
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